Conventionally, it is well-known that a hydraulic control valve adjusts a pressure of an operating fluid (hydraulic oil) according to a movement of a spool. As shown in FIG. 12, the hydraulic control valve includes a sleeve 110 having a spool hole 100, and a spool 120 inserted into the spool hole 100 and being slidable relative to the sleeve 110 in an axial direction of the sleeve 110. The axial direction of the sleeve 110 is parallel to a valve-closing direction and a valve-opening direction as shown in FIG. 12. The sleeve 110 is provided with plural hydraulic ports including an inlet port 130 and an outlet port 140. A communication between the inlet port 130 and the outlet port 140 is allowed or interrupted according to a movement of the spool 120.
When the spool 120 is moved in the valve-opening direction to open the inlet port 130, an opening of the inlet port 130 is slightly opened that an opening quantity of the inlet port 130 changes from zero to a positive value. In this case, as shown in FIG. 13, a flow quantity of the hydraulic fluid indicated by a solid line and a fluid force of the hydraulic fluid in the axial direction indicated by a dotted line are sharply increased. Therefore, a variation of the hydraulic fluid is generated, and a control of the hydraulic fluid becomes unstable. The fluid force is a pressure of the hydraulic fluid which disturbs the movement of the spool 120 in a case where the spool 120 is moved in the valve-opening direction.
According to JP-60-125471A, a notch shaped portion or a tilted shaped portion starting from an edge portion is provided on an entire periphery of the edge portion, so as to suppress the variation of the hydraulic fluid at a time point that the opening of the inlet port 130 is slightly opened. The edge portion is a hydraulic dividing portion of the spool 120.
According to JP-2012-255508A, a straight step shaped portion is provided at a position right downstream of an edge portion.
However, when a solenoid is used as an actuator driving the spool 120, a control stroke of the solenoid is limited. In other words, a movable range of a plunger that is a stroke range of the spool 120 is limited. When the notch shaped portion, the tilted shaped portion, or the straight step shaped portion is provided in the stroke range, an opening width of the inlet port 130 opened by the spool 120 is insufficient. The opening width is referred to as a fully open stroke. As shown in FIG. 14, since a maximum flow quantity of the hydraulic fluid of when the inlet port 130 is opened to the fully open stroke becomes smaller, a required flow performance is deteriorated. It is possible that the fully open stroke becomes larger by increasing in size of a magnetic circuit portion of the solenoid to increase a control stroke. However, in this case, since the hydraulic control valve is increased in size, a mountability is deteriorated.
As a dotted line shown in FIG. 14, in an opening area exceeding the notch shaped portion, the tilted shaped portion, or the straight step shaped portion, since an injection flow of the hydraulic fluid flowing into the inlet port 130 flows in a direction toward the axial direction, the fluid force negatively affects a stability of an action of the hydraulic control valve.